Influence of soil solution aluminum on root elongation of wheat seedlings

Wheat (Triticum aestivum L.) seedlings were grown for 4 days in an acid soil horizon treated with 10 levels each of Ca(OH)₂, CaSO₄ and CaCl₂. The treatments resulted in a wide range of Al levels and Al speciation in soil solution. Seedling root length in the Ca(OH)₂ treatments was significantly related (p<0.01) to calculated Al³⁺ activity in soil solution. The Al–SO₄ complex in soil solution had a negligible effect on the root growth of Hart wheat, thus confirming the previously reached conclusion concerning the nonphytotoxicity of Al–SO₄. The short-term seedling root growth technique used in this investigation allowed for separation of Al effects on root elongation from those on plant nutrition and should be useful for studying Al toxicity relationships in soil.     

二氧化硫增强拟南芥植株对干旱的适应性

以模式植物拟南芥为材料,研究SO_2对植物干旱适应性的影响。采用分光光度法检测植物干旱生理指标的变化,并用半定量RT-PCR技术分析了拟南芥热激基因和干旱响应基因的转录水平。研究发现:4周龄拟南芥植株暴露于30mg/m3的SO_2后,6—72h间叶面气孔开度显著低于对照并逐渐减小,在暴露48h和72h时,热激转录因子HsfA2和热激基因Hsp17.7、Hsp17.6B、Hsp17.6C转录上调,干旱响应基因DREB2A、DREB2B和RD29A表达增强;在SO_2熏气72h后进行干旱胁迫,干旱期间SO_2预暴露植株的叶片相对含水量高于非熏气干旱处理组,植株萎蔫程度比后者明显减轻,且SO_2预暴露植株的地上组织中可溶性糖和脯氨酸含量升高,超氧化物歧化酶活性提高,丙二醛含量降低。结果表明:SO_2能降低气孔开度、提高抗氧化能力、上调热激基因和干旱响应基因转录,并能促进干旱期间植物细胞内渗透调节物质的合成和积累,促使抗氧化酶活性提高,从而降低干旱胁迫对植株造成的氧化损伤,增强拟南芥对干旱的适应性。植物通过基因转录应答、酶活性改变、渗透调节物质积累等,在适应环境高浓度SO_2的同时,提高了对干旱的适应性。     

Influence of pH,exchangeable aluminium and 0.02M CaCl2-extractable aluminium on the growth and nitrogen-fixing activity of white clover (Trifolium repens) in some New Zealand soils

The effects of soil acidity on the growth and N₂-fixing activity of white clover in seven acid topsoils and subsoils of New Zealand were investigated using a glasshouse experiment.The application of phosphate (Ca(H₂PO₄)₂) to the soils resulted in very large increases in white clover growth on all soils. The application of phosphate, as well as increasing P supply, also decreased 0.02M CaCl₂-extractable Al levels, but had little effect on exchangeable Al levels.Where adequate phosphate was applied, increasing rates of lime (CaCO₃) resulted in increased plant growth on most soils. N₂[C₂H₂]-fixing activity was increased by the first level of lime for one soil, but generally remained approximately constant or declined slightly at higher rates of lime. Up to the point of maximum yield, white clover top weight was more highly correlated with 0.02M CaCl₂-extractable soil Al than with exchangeable Al or pH. At pH values greater than 5.5, plant yield declined on some soils, apparently because of Zn deficiency. The data suggest that white clover is unlikely to be affected by Al toxicity at 0.02M CaCl₂-extractable Al levels of less than about 3.3 g g^–1. However, there were differences between soils in apparent plant tolerance to 0.02M CaCl₂-extractable Al, which appeared to be caused by differing C levels in the 0.02M CaCl₂ extracts.     

Effects of litter incorporation and nitrogen fertilization on the contents of extractable aluminium in the rhizosphere soil of tea plant (Camallia sinensis (L.) O. Kuntze)

The effects of litter incorporation and nitrogen application on the properties of rhizosphere and bulk soils of tea plants (Camellia sinensis (L.) O. Kuntze) were examined in a pot experiment. Total of 8 treatments included four levels of tea litter additions at 0, 4.9, 9.8, and 24.5 g kg^–1 in combination with two N levels (154.6 mg kg^–1 and without). After 18 months of growth the rhizosphere soil was collected by removing the soil adhering to plant roots and other soil was referred to as bulk soil. The dry matter productions of tea plants were significantly increased by N fertilization and litter incorporation. The effect of litter was time-depending and significantly decreased the content of exchangeable Al (Al_ex, by 1 mol L^–1 KCl) and Al saturation at 9 months after litter incorporation whereas soil pH was not affected, although the litter contained high Al content. After 18 months, the contents of extractable Al by dilute CaCl₂, CuCl₂ + KCl, NH₄OAC, ammonium oxalate and sodium citrate (Al_CaCl2, Al_Cu/KCl, Al_NH4OAC, Al_Oxal, and Al_Cit respectively) and Al_ex, were not affected by litter application, except that of Al_CaCl2 in the rhizosphere soil which was decreased following litter additions. Nitrogen fertilization with NH₄ ⁺ (urea and (NH₄)₂SO₄) significantly reduced soil pH, the contents of exchangeable Ca, K, Mg and base saturation while raised extractable Al levels (Al_CaCl2, Al_Cu/KCl, Al_NH4OAC, and Al_ex). In the rhizosphere soils exchangeable K accumulated in all treatments while exchangeable Ca and Mg depleted in treatments without litter application. The depletions of Ca and Mg were no longer observed following litter incorporation. This change of distribution gradients in rhizosphere was possibly due to the increase of nutrient supplies from litter decomposition and/or preferable root growth in soil microsites rich in organic matter. Lower pH and higher extractable Al (Al_CaCl2, Al_ex, and Al_NH4OAC) in the rhizosphere soils, regardless of N and litter treatments, were distinct and consistent in all treatments. Such enrichments of extractable Al in the rhizosphere soil might be of importance for tea plants capable of taking up large amounts of Al.     

Effects of plant species on phosphorus availability in a range of grassland soils

Vegetative conversion from grass to forest may influence soil nutrient dynamics and availability. A short-term (40 weeks) glasshouse experiment was carried out to investigate the impacts of ryegrass (Lolium perenne) and radiata pine (Pinus radiata) on soil phosphorus (P) availability in 15 grassland soils collected across New Zealand using ³³P isotopic exchange kinetics (IEK) and chemical extraction methods. Results from this study showed that radiata pine took up more P (4.5–33.5 mg P pot^–1) than ryegrass (1.1–15.6 mg pot^–1) from the soil except in the Temuka soil in which the level of available P (e.g., E _1min P_i, bicarbonate extractable P_i) was very high. Radiata pine tended to be better able to access different forms of soil P, compared with ryegrass. There were no significant differences in the level of water soluble P (Cp, intensity factor) between soils under ryegrass and radiata pine, but the levels of Cp were generally lower compared with original soils due to plant uptake. The growth of both ryegrass and radiata pine resulted in the redistribution of soil P from the slowly exchangeable P_i pool (E _{> 10m} P_i, reduced by 31.8% on the average) to the rapidly exchangeable P_i (E _1min-1d P_i, E _1d-10m P_i) pools in most soils. The values of R/r ₁ (the capacity factor) were also generally greater in most soils under radiata pine compared with ryegrass. Specific P mineralisation rates were significantly greater for soils under radiata pine (8.4–21.9%) compared with ryegrass (0.5–10.8%), indicating that the growth of radiata pine enhanced mineralisation of soil organic P. This may partly be ascribed to greater root phosphatase activity for radiata pine than for ryegrass. Plant species × soil type interactions for most soil variables measured indicate that the impacts of plant species on soil P dynamics was strongly influenced by soil properties.     

Interactions of calcium sulfite with soils and plants

CaSO₃ is a by-product formed by several of the processes used for scrubbing SO₂ from flue gas produced by coal-burning power generators. Using CaSO₃ to improve the calcium status of acid soils would be a beneficial alternative to disposal in landfills. CaSO₃ has biocidal properties and is used as a disinfectant and food and drink preservative. It is important to evaluate under what conditions application to soils would not harm plant growth. Laboratory experiments confirmed that two transformations of CaSO₃ occurred in soil systems: (1) decomposition to produce SO₂ gas, and (2) oxidation to calcium sulfate. Conversion to SO₂ occurred in solution and soil at low pH, and acid soils treated with CaSO₃ were initially toxic to seedling root growth. The degree of toxicity was time-dependent, with reduction in toxicity occurring as CaSO₃ oxidized to calcium sulfate. Soil reaction also influenced toxicity, and at soil pH levels above 6, little seedling toxicity was evident.     

Environmental gradients,plant distribution,and species richness in arctic salt marsh near Prudhoe Bay,Alaska

Spatial patterns of plant cover and species composition in arctic salt marsh and salt affected tundra near Prudhoe Bay, Alaska reflect gradients in elevation, soil conductivity, and soil concentrations of the ions prevalent in seawater. Soil conductivity and soil concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ⁼ and Cl^– were significantly related to site elevation, decreasing as elevation increased. Vascular plant species richness increased significantly as soil conductivity and soil ion concentrations decreased, and site elevation increased. Puccinellia phryganodes was the only species present in low elevation sites with low plant cover, high soil conductivity and high soil concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ⁼ and Cl^–. Mid-gradient sites were dominated by Carex subspathaceae. Plant cover at these sites was greater than at lower elevation sites, but bare ground was still present. Higher elevation sites had the lowest concentrations of soil ions and the lowest soil conductivities. These sites had little bare ground, contained as many as 16 species, and were dominated by Dupontia fischeri and Eriophorum angustifolium. Ordinations indicated that a complex topographic gradient related most closely to elevation and site distance from the coast best explains variation in the vegetation cover. Irregular deposition along the coastline partially or completely buried three sites in peat or sand up to 20 cm deep. Such rapid changes in plant cover and species composition contributes to the community patch mosaic typical of these marshes. Results suggest an individualistic response of plant species to the environmental gradients in salt marsh and salt affected tundra and are indicative of successional models developed in other marginal arctic environments.     

Amelioration of acid soil infertility by phosphogypsum

Amelioration of subsoil acidity requires an increase in Ca status along with a decrease in Al status in subsoil. In this study, effects of phosphogypsum (PG) on the amelioration of subsoil acidity have been evaluated, using cultivated and woodland subsoils representing Cecil, Wedowee (both Typic Hapludult) and Bladen (Typic Albaquult) series. Subsoil (0.6–0.8 m) samples were collected and treated with either PG (approximately 2 Mg ha^-1 rate), Ca(NO₃)₂ or Mg(NO₃)₂ along with an unamended control treatment. A fertile topsoil amended with NH₄NO₃ was placed on top of all treated subsoil. Top and root growth of alfalfa [Medicago sativa (L.) cv. Hunter River] and soybean [Glycine max (L.) Merr. cv. Lee] were significantly greater in PG-amended than in unamended pots of the Cecil and Wedowee soils, although most growth was observed with the Ca(NO₃)₂-amended treatment. In the Bladen soil, however, none of the amendments evoked a significant growth response in either alfalfa or soybean. The concentration of Ca in the displaced soil solution (in soils with no plants) as well as tissue levels of Ca suggest that the growth response was partly due to an improved Ca availability in both PG or Ca(NO₃)₂-treated soils. Exchangeable Al decreased in PG-amended soils. The self-liming effect of PG, which is a release of OH^- due to ligand exchange between SO₄ ^2- and OH^-, as well as a decrease in exchangeable Al in PG-amended soil is greater in predominantly kaolinitic Cecil and Wedowee soils than in smectitic Bladen soil. As a result, significant growth response to PG amendment was observed in the Cecil and Wedowee soils, but not in the Bladen soil.     

Effects of cadmium and nickel on in vivo carbon dioxide exchange rate of pigeon pea (Cajanus cajan L.)

Effects of acidic soil factors (Al, H-ion, Mo, and Mn) upon the soybean (Glycine max (L.) Merr. cv. Essex)/Bradyrhizobium japonicum symbiosis were examined in acidified soil. Plants were grown under full sunlight in pots containing N-deficient soil (pH 6.7) or similar soil amended with sufficient Al₂(SO₄)₃ or elemental S to give soil pH values of 4.8 and 4.6, respectively, and water-extractable Al levels of 30 and 14 M, respectively. Other treatments consisted of the addition of inorganic N or inoculation with commercial or locally-isolated B. japonicum. Acidification did not reduce shoot or root weights of plants receiving inorganic N but reduced (P0.05) shoot and root dry weights, nodule dry weights and numbers, shoot N concentrations, and chlorophyll levels of inoculated plants. Shoot dry weights and nodulation of inoculated plants were greater (P0.05) in Al₂(SO₄)₃-amended soil than in S-amended soil. Addition of Mo was not beneficial. It was concluded that reduced plant growth was caused by the effects of acidified soil on nodulation and that H-ion toxicity was probably the most limiting factor. Effects of Al, Mn, or Mo appeared less likely.     

Tolerance ofPinus densiflora,Pinus thunbergii,andLarix leptolepis seedlings to SO2

Summary Effects of exposure to SO₂ at 0.5, 1.0, and 1.5 ppm for 48 hours on sulfur uptake, needle injury, height growth, diameter growth, dry weight increment, and relative growth rate of seedlings of three species of gymnosperms were investigated in a controlled environment. On the basis of such responses as needle injury, dry weight increment, relative growth rate, and diameter growth, tolerance to SO₂ 60 days after treatment varied in the following order:Pinus thunbergii (most tolerant),Pinus densiflora, Larix leptolepis (least tolerant). On the basis of height growth response the order of SO₂ tolerance was:Pinus densiflora>Pinus thunbergii>Larix leptolepis. The range of response to SO₂ of the three species varied with the specific response measured. The usefulness of relative growth rate as a pollution response is emphasized because of differences among species in initial size and growth rate. Limitations of using height growth responses to determine pollution tolerance are discussed. Caution is advised in constructing tables of pollution tolerance of plants by using data of investigators who apply different criteria for assessing plant responses to air pollution.Research supported by the College of Agricultural and Life Sciences, University of Wisonsin, Madison, Wisconsin, USA and by Yamagata University, Tsuruoka, Japan. McIntyre-Stennis, Project 2599.     

Growth,net photosynthesis and leaf nutrient status of <Emphasis Type="Italic">Fagus crenata</Emphasis> seedlings grown in brown forest soil acidified with H<Subscript>2</Subscript>SO<Subscript>4</Subscript> or HNO<Subscript>3</Subscript> solution

To obtain basic information for evaluating critical loads of acid deposition for protecting Japanese beech forests, growth, net photosynthesis and leaf nutrient status of Fagus crenata seedlings grown for two growing seasons in brown forest soil acidified with H₂SO₄ or HNO₃ solution were investigated. The whole-plant dry mass of the seedlings grown in the soil acidified by the addition of H₂SO₄ or HNO₃ solution was significantly less than that of the seedlings grown in the control soil not supplemented with H⁺ as H₂SO₄ or HNO₃ solution. However, the degrees of reduction in the whole-plant dry mass and net photosynthetic rate of the seedlings grown in the soil acidified by the addition of H⁺ as H₂SO₄ solution at 100 mg l^–1 on the basis of air-dried soil volume (S-100 treatment) were greater than those of the seedlings grown in the soil acidified by the addition of H⁺ as HNO₃ solution at 100 mg l^–1 (N-100 treatment). The concentrations of Al and Mn in the leaves of the seedlings grown in the S-100 treatment were significantly higher than those in the N-100 treatment. A positive correlation was obtained between the molar ratio of (Ca+Mg+K)/(Al+Mn) in the soil solution and the relative whole-plant dry mass of the seedlings grown in the acidified soils to that of the seedlings grown in the control soil. Based on the results, we concluded that the negative effects of soil acidification due to sulfate deposition are greater than those of soil acidification due to nitrate deposition on growth, net photosynthesis and leaf nutrient status of F. crenata, and that the molar ratio of (Ca+Mg+K)/(Al+Mn) in soil solution is a suitable soil parameter for evaluating critical loads of acid deposition in efforts to protect F. crenata forests in Japan.     

喀斯特地区野生毛葡萄的钙组分特征及其对高钙环境的适应性分析北大核心CSCD

为了探究喀斯特地区野生毛葡萄(Vitis quinquangularis Rehd.)器官的钙含量、组分及其分布特征,揭示野生毛葡萄的需钙特性及其对高钙土壤的适应机制。该研究以贵州喀斯特地区野生毛葡萄为材料,取样测定了40个样地的野生毛葡萄立地土壤的pH值、交换性钙含量及其根、茎、叶中钙和镁及其钙组分含量,分析土壤交换性钙含量与不同钙组分间的关系,并观察野生毛葡萄叶片表面及根、茎、叶中的钙晶体。结果表明:(1)喀斯特地区野生毛葡萄总钙含量在器官中的分布表现为叶>根>茎,其分布特征与喜钙植物类似。(2)野生毛葡萄根、茎、叶中主要钙组分含量由高到低依次基本为草酸钙、果胶酸钙、水溶性钙、磷酸钙+碳酸钙、硝酸钙+氯化钙、硅酸钙(茎中稍有不同),根、茎、叶中草酸钙占所有钙组分总量和总钙含量的比例均最高,其次是果胶酸钙。(3)各样地野生毛葡萄叶片中Ca+Mg的含量范围在1.30%~4.07%之间,绝大多数在3.0%~4.0%范围内,表现出喜钙植物叶中高Ca+Mg含量的特性。(4)在喀斯特地区的野生毛葡萄体内,多种钙组分含量与土壤中的钙含量呈显著或极显著的正相关关系。(5)扫描电镜观察发现,野生毛葡萄叶片和根中储存有大量的草酸钙晶体,叶片中的草酸钙可通过气孔排出体外。研究发现,喀斯特地区野生毛葡萄属于喜钙植物,对喀斯特高钙环境的适应性强,叶片中钙的富集量大,有大量的草酸钙和果胶酸钙储存于体内,这种储钙特性和气孔的排钙行为对野生毛葡萄适应高钙环境具有重要作用。     

披针叶黄华试管苗适应盐胁迫的渗透调节机制

以披针叶黄华(Thermopsis lanceolata)试管苗为材料,通过组培方法研究其在0、0.2%、0.4%、0.6%、0.8%和1.0%NaCl和Na2SO4胁迫30d后的生长、有机渗透调节物质和无机渗透调节物质(Na+、K+和Ca2+)含量的变化,以探讨其耐盐性机制。结果显示:(1)随NaCl和Na2SO4胁迫浓度的增加,披针叶黄华试管苗叶片脯氨酸和可溶性糖含量均显著持续增加,且NaCl胁迫下脯氨酸上升的幅度均大于相同浓度Na2SO4胁迫下的增幅,而可溶性糖上升的幅度却小于相同浓度Na2SO4胁迫下的幅度;可溶性蛋白含量随NaCl浓度的增大呈先升高后降低的趋势,但随Na2SO4浓度的增加呈持续上升的趋势。(2)随NaCl和Na2SO4浓度的增加,披针叶黄华试管苗Na+含量呈增加趋势且各处理均显著高于对照,Ca2+含量和叶片K+含量却呈逐渐减少趋势且各处理均显著低于对照,而根系K+含量呈先降后升的趋势;Na2SO4胁迫下披针叶黄华试管苗叶片Na+含量上升幅度以及K+和Ca2+含量下降幅度均明显低于相同浓度NaCl胁迫组;而Na+/K+和Na+/Ca2+比值随NaCl和Na2SO4浓度增加而升高;NaCl胁迫下,叶片Na+/K+和Na+/Ca2+高于相同浓度Na2SO4胁迫下的比值,而根系Na+/K+和Na+/Ca2+却低于相同浓度Na2SO4胁迫下的比值。研究表明,盐胁迫下,披针叶黄华试管苗通过抑制叶片中Na+积累并增加可溶性糖和可溶性蛋白含量,在根系中维持较高K+和Ca2+含量以及较低水平Na+/K+和Na+/Ca2+比,以降低披针叶黄华细胞渗透势来适应盐渍环境;披针叶黄华对NaCl胁迫的调节能力弱于Na2SO4。     

Effect of H2SO4, HCl and Al2(SO4)3 on the yield,chemical composition and Ca uptake from applied Ca45CO3 by dhaincha (Sesbania aculeata Pers.) in a saline alkali soil

Summary Application of CaCO₃ and a lime-solubilizing agent (viz H₂SO₄, HCl, and Al₂(SO₄)₃) to a saline-alkali soil caused a significant increase in the dry matter yield of dhaincha (Sesbania aculeata Pers). The extent of yield enhancement by these amendments was in the decreasing order: HCl, H₂SO₄ and Al₂(SO₄)₃. Calcium content in the plant increased significantly with the application of these amendments and it was in the decreasing order: H₂SO₄, Al₂(SO₄)₃ and HCl. The uptake of Ca from native CaCO₃ was much less than that from the added Ca⁴⁵CO₃. Phosphorus content in the plant increased with the HCl and H₂SO₄ treatments and decreased with the Al₂(SO₄)₃ treatments. Nitrogen and Na contents decreased with the addition of these amendments. re]19730521     

Growth of Trifolium alpinum: Effects of soil properties, symbionts and pathogens

The lowland cultivation of Trifolium alpinum, a clover species found on acid soils in the Alps and suitable for the restoration of erosion areas at high altitudes, failed repeatedly in previous experiments. Three experiments were carried out in a controlled environment to elucidate the reasons for the failure and to develop possible cultivation strategies. In experiment I, T. alpinum was grown in an autochthonous soil from the Alps (high elevation) and in two allochthonous soils, a grassland soil from the Hercynian mountains (medium elevation), and an arable soil (low elevation), in which the seed propagation of T. alpinum had failed previously. The two allochthonous soils had lower contents of soil organic C and ergosterol, an indicator for fungal biomass, than the autochthonous high-elevation soil, but higher levels of exchangeable Ca and extractable P. Plants grown in the allochthonous soils achieved higher biomass and total N amounts per plant than those from the high elevation soil if inoculated with this autochthonous material to establish rhizobial infection. In the allochthonous high elevation soil, the growth of T. alpinum was P-limited as shown in experiment II. In experiment I, plants grown in the low elevation soil had a lower biomass and smaller number of active leaves at 120 days after emergence than those grown on the medium elevation soil. This difference can be explained by strong colonization with the phytophagous nematode Pratylenchus sp., as demonstrated in experiment III by comparing plant growth either in untreated or in autoclaved low-elevation soil. Successful propagation of T. alpinum at low elevation may be achieved through suitable inoculation with autochthonous soil biota, especially Rhizobia, and avoidance of soils infested by Pratylenchus species by choosing sites with acidic soil and ensuring adequate P-availability.     

Effect of soil K, Ca and Mg saturation and endomycorrhization on growth and nutrient uptake of sugar maple seedlings

Nutrient imbalances of declining sugar maple (Acer saccharum Marsh.) stands in southeastern Quebec have been associated with high exchangeable Mg levels in soils relative to soil K and Ca. A greenhouse experiment was set up to test the hypothesis that the equilibrium between soil exchangeable K, Ca, and Mg ions influences the growth and nutrient status of sugar maple seedlings. Also tested was whether endomycorrhization can alter nutrient acquisition under various soil exchangeable basic cations ratios. Treatments consisted of seven ratios of soil exchangeable K, Ca, and Mg making up a total base saturation of 58%, and a soil inoculation treatment with the endomycorrhizal fungus Glomus versiforme (control and inoculated), in a complete factorial design. Sugar maple seedlings were grown for 3 months in the treated soils. Plant shoot elongation rate, dry biomass and nutrient concentrations in foliage were influenced by the various ratios of soil cations. The predicted plant biomass and foliar K concentration were highest at a soil Ca saturation of 38%, a soil K saturation of 12%, and a soil Mg saturation of 8%. Potassium concentration in foliage was dependent on the level of Ca and Mg saturation in the soil when soil K saturation was close to 12%. Foliar Ca and Mg levels were more dependent on their corresponding levels in soil than foliar K. Colonization by G. versiforme did not influence seedling growth and macronutrient uptake. The results confirm that growth and nutrition of sugar maple are negatively affected by imbalances in exchangeable basic cations in soils.     

Short-Term Salinity Induced Changes in Two Wheat Cultivars at Different Growth Stages

Soluble sugars, proline, total chlorophyll contents and electrolyte leakage were measured in two wheat (Triticum aestivum L.) cultivars KRL 1-4 and HD 2009 at different growth stages [crown root initiation (CRI), flowering, and soft dough] under short term salinity (NaCl, CaCl₂ and Na₂SO₄). In control plants sugar contents were maximum at flowering stage. Proline and sugar concentrations increased in both cultivars under salinity with a maximum increase at CRI. Electrolyte leakage increased and chlorophyll content decreased with the plant age. A sharp increase of electrolyte leakage was noticed at salinity of 10 and 15 dS m^–1 in HD 2009 and KRL 1-4, respectively. The short-term salinity at CRI stage proved more detrimental as compared to salinity at flowering and soft dough stages in term of all biochemical changes induced. In wheat, plant resistance to salinity increased with the age of plant. The cultivar KRL 1-4 performed better under salinity as compared to HD 2009.     

Simulated effects of atmospheric sulfur deposition on nutrient cycling in a mixed deciduous forest

The effects of three S deposition scenarios — 50% reduction, no change, and 100% increase — on the cycles of N, P, S, K, Ca, and Mg in a mixed deciduous forest at Coweeta, North Carolina, were simulated using the Nutrient Cycling model (NuCM). The purpose of this exercise was to compare NuCM's output to observed soil and streamwater chemical changes and to explore NuCM's response to varying S deposition scenarios. Ecosystem S content and SO₄ ^2– leaching were controlled almost entirely by soil SO₄ ^2– adsorption in the simulations, which was in turn governed by the nature of the Langmuir isotherm set in the model. Both the simulations and the 20-year trends in streamwater SO₄ ^2– concentration suggest that the ecosystem is slowly becoming S saturated. The streamwater data suggest S saturation is occurring at a slower rate than indicated by the simulations, perhaps because of underestimation of organic S retention in the model. Both the simulations and field data indicated substantial declines in exchangeable bases in A and BA soil horizons, primarily due to vegetation uptake. The correspondence of model output with field data in this case was a result of after-the-fact calibration (i.e. setting weathering rates to very low values) rather than prediction, however. Model output suggests that soil exchangeable cation pools change rapidly, undergoing annual cycles and multi-decade fluctuations.Varying S deposition had very little effect upon simulated vegetation growth, nutrient uptake, or N cycling. Varying S deposition strongly affected simulated Ca²⁺. Mg²⁺, K⁺, and P leaching but caused little change in soil exchangeable pools of Ca²⁺ K⁺, or P because soil exchangeable pools were large relative to fluxes. Soil exchangeable Mg²⁺ pools were reduced by high rates of S deposition but remained well above levels sufficient for tree growth. Although the total soil pools of exchangeable Ca²⁺ and K⁺ were only slightly affected by S deposition, there was a redistribution of Ca²⁺ and K⁺ from upper to lower horizons with increasing S deposition, causing increased base saturation in the deepest (BC) horizon. The 100% increased S deposition scenario caused increasing peaks in simulated Al³⁺ concentrations in A horizons after 25 years as a result of large seasonal pulses of SO₄ ^2– and lowered base saturation. Simulated soil solution Al³⁺ concentrations remained well below toxicity thresholds for selected tree species at the site.     

黄河口湿地柽柳灌丛土壤盐渍化特征

为探究黄河三角洲湿地柽柳灌丛下土壤的盐渍化特征,在黄河三角洲国家级自然保护区(37°35''-12''N,118°33''-119°20''E)黄河入海口附近,根据长势基本一致的原则分别在碱蓬群落、柽柳群落和芦苇群落各选3株柽柳,采集柽柳灌丛下土壤样品,分析土壤盐分和盐碱化参数的空间分布以及距基茎不同距离处研究对象(土壤总盐(TS)、电导率(EC)、pH、交换性钠百分率(ESP))和环境因子(Na⁺、K⁺、Ca²⁺、Mg²⁺、Cl^-、HCO₃^-、SO^2-₄)之间的关系。结果表明：(1)研究区土壤为弱碱化盐土,离子含量由高到低依次为Cl^->Na⁺>SO^2-₄ >Ca²⁺>Mg²⁺>HCO^-₃>K⁺。除pH在土壤表层数值最低外,表层土壤TS、EC、ESP和盐分离子大于深层土壤,显示表聚性。(2)土壤盐分和盐碱化参数空间分布总体为：在柽柳基茎周围形成"盐谷"、"碱谷"效应, Na⁺、Mg²⁺、Cl^-表现为"盐谷",K⁺ 、SO^2-₄ 、Ca²⁺ 表现为"盐岛"。(3)在整个土壤剖面中,与TS、EC相关性最强的阴阳离子为Mg²⁺、Cl^-,从灌丛中心到灌丛间裸地Ca²⁺、SO^2-₄与TS、EC的相关性逐渐减弱,Mg²⁺、Cl^-与TS、EC的相关性逐渐增强。Ca²⁺和SO^2-₄与pH表现为较强的负相关性;与ESP相关性最强的阴离子为HCO^-₃,与之相关性最强的阳离子为Na⁺和K⁺,并且Na⁺和K⁺与ESP的相关性表现出从灌丛中心向外逐渐增强。(4)土壤盐渍化主要受控于Na⁺,从灌丛下到灌丛间裸地Cl^-对盐渍化程度的影响逐渐增加,SO^2-₄的影响逐渐降低。     

Suppression of nitrification and nitrous oxide emission by the tropical grass Brachiaria humidicola

Nitrification by soil nitrifiers may result in substantial losses of applied nitrogen through NO₃ ^– leaching and N₂O emission. The biological inhibition of nitrification by crop plants or pasture species is not well known. This study was conducted to evaluate the ability of three pasture species, Brachiaria humidicola, B. decumbens and Melinis minutiflora to inhibit nitrification. Plants were grown in a growth chamber for sixty days, fertilized with (NH₄)₂SO₄. After harvesting, the soil was incubated with (NH₄)₂SO₄ for 24 days. Ammonium oxidizing bacteria (AOB), NH₄-N levels, and N₂O emission were monitored at 4 d intervals. Among the species studied, B. humidicola inhibited nitrification and maintained NH₄-N in soil to a much greater extent than the other two species. This nitrification inhibition lasted for 12 days after initiation of soil incubation study (i.e. from 60 DAS when the plants were harvested). The AOB populations and N₂O emission from the soil were significantly lower in the soils where B. humidicola has been grown compared to the other two species. Root exudates and soil extracts of B. humidicola suppressed AOB populations, whereas those of B. decumbens and M. minutiflora did not. The results are in consistence with the hypothesis that B. humidicola suppressed nitrification and N₂O emissions through an inhibitory effect on the AOB population.